Hypothesis\n\nIn aging neurons, boosting upstream base excision repair (BER) glycosylases such as OGG1 without a concurrent increase in downstream AP‑site processing enzymes (APE1, DNA polymerase β, Ligase III) leads to accumulation of toxic abasic (AP) sites that trigger cGAS‑STING‑dependent neuroinflammation independently of mitochondrial DNA release.\n\n### Mechanistic rationale\n\n- OGG1 excises 8‑oxoguanine, generating an AP site 1.\n- APE1 normally cleaves the AP site to allow repair synthesis; its activity declines with age 2.\n- When APE1 is limiting, AP sites persist, can be converted to single‑strand breaks during replication or transcription, and are sensed by cGAS as cytosolic DNA 3.\n- Persistent AP sites also stall DNA polymerase β, fostering a toxic oxidation‑excision cycle that can expand repeat sequences 4.\n\n### Testable predictions\n\n1. In cultured aged mouse hippocampal neurons, adenoviral overexpression of OGG1 alone will increase AP‑site levels (measured by aldehyde‑reactive probe) and elevate cytosolic cGAS activation (phospho‑STING, IFN‑β mRNA) compared with controls.\n2. Co‑overexpression of OGG1 and APE1 (or OGG1, Pol β, Ligase III) will normalize AP‑site burden and suppress cGAS‑STING signaling despite comparable reductions in 8‑oxoguanine.\n3. Pharmacological inhibition of APE1 in young neurons treated with an OGG1 agonist will recapitulate the inflammatory phenotype seen in aged cells.\n\n### Experimental design\n\n- Models: Primary hippocampal neurons from 3‑month (young) and 24‑month (aged) mice; optionally human iPSC‑derived neurons subjected to oxidative stress.\n- Interventions: Adeno‑associated virus (AAV) vectors for OGG1, APE1, Pol β, Ligase III; small‑molecule OGG1 agonist (e.g., CBH2); APE1 inhibitor (ethoxyquin) as control.\n- **Readouts": \n * 8‑oxoguanine (immunofluorescence, slot blot).\n * AP‑site aldehyde‑reactive probe staining and flow cytometry.\n * Cytosolic DNA sensing (cGAS phosphorylation, STING dimerization, IFN‑β ELISA).\n * Mitochondrial DNA release (qPCR of cytosolic mtDNA).\n * Neuroinflammatory markers (IL‑1β, TNF‑α, Iba1 activation in co‑culture microglia).\n * Neuronal health (MAP2 integrity, LDH release, electrophysiological LTP in slices).\n- Analysis: Compare groups using two‑way ANOVA (age × treatment) with post‑hoc tests; falsify hypothesis if OGG1 overexpression alone does not raise AP‑site levels or cGAS‑STING activation, or if downstream co‑overexpression fails to rescue inflammation.\n\n### Potential outcomes\n\n- Support: OGG1‑only increase AP sites and STING signaling; dual overexpression restores homeostasis and reduces inflammation without worsening repeat expansions.\n- Refutation: OGG1 overexpression reduces 8‑oxoguanine and inflammation regardless of APE1 levels, indicating AP sites are not pathogenic; or downstream overexpression exacerbates toxicity, suggesting alternative bottlenecks.\n\n### Implications\n\nIf validated, the hypothesis would shift therapeutic focus from unilateral glycosylase activation to balanced BER pathway enhancement, informing combination strategies that pair OGG1 activators with APE1 or polymerase β boosters to avoid generating harmful repair intermediates.